Turbo machines, such as gas turbine engines, have one or more turbine modules, each of which includes a plurality of blades and vanes for exchanging energy with the working medium fluid. Some of the vanes may be fixed and others may be variable, that is, rotatable between positions in the gas turbine engine. A typical vane known in the prior art is shown in FIG. 5 and comprises, generally, a trunnion portion (a) and an airfoil portion (b). The airfoil portion comprises a leading edge (d) and a trailing edge (e). The trunnion portion (a) has an enlarged button portion (f) proximate to a transition zone (g) between the trunnion and airfoil. The variable vane in operation is mounted for rotation about axis (c) so as to locate the position of the leading edge of the airfoil as desired. Generally, the variable vane is rotated through an angle of about 40xc2x0.
Because the vanes of a gas turbine engine operate in a hostile environment, they are subjected to significant stresses, both steady stress and vibratory stress. The design of variable vanes of the prior art are such that the transition zone (g) from the trunnion portion (a stiff section of the variable vane) to the airfoil portion of the vane (a flexible section of the variable vane) is subjected to high stresses which may lead to failure of the vane at the transition area and subsequent catastrophic damage to the gas turbine engine.
Naturally, it would be highly desirable to provide a vane configuration which would reduce stress in the transition zone between the stiff portion (the trunnion) and the flexible portion (the airfoil) and provide a substantially smooth and continuous reduction in stress at the transition zone from the trunnion portion to the airfoil portion.
Accordingly, it is a principal object of the present invention to provide a vane which has reduced stress at the transition zone between the stiff section (trunnion) of the variable vane and the flexible section (airfoil) of the vane.
It is a further object of the present invention to provide in the transition zone of a variable vane a smooth and continuous reduction in stress from the stiff (trunnion) portion to the flexible (airfoil) portion of the variable vane.
It is an additional object of the present invention to provide a vane which discourages air flow from the pressure side to the suction side of the vane.
It is a still further object of the present invention to provide a variable vane useful in gas turbine engines which may be casted.
In accordance with the present invention, the vane comprises a trunnion portion and an airfoil portion, the airfoil portion is defined by a leading edge, a trailing edge, and a pair of side edges. One or more of the side edges comprises a fin which extends from proximate to the trunnion portion toward the trailing edge of the airfoil portion. The fin tapers in thickness from the trunnion portion to the trailing edge portion. The fin may extend above and/or below the top and bottom surfaces of the airfoil. The fin may be formed on a portion of one or both of the side edges.
The vane design in accordance with the present invent-on offers a number of benefits. Firstly, the provision of the fin allows for a smooth transition from the trunnion portion to the airfoil portion where the transition is formed of a thicker cross section than the airfoil itself thereby reducing stresses which normally would occur on the airfoil in the absence of the fin structure. Secondly, the design of the fin on the airfoil of the vane of the present invention substantially eliminates air flow from the pressure side of the airfoil to the suction side of the airfoil which is undesirable.